1. Technical Field
The invention relates to an electrophotographic photoreceptor, and an image forming apparatus and a process cartridge using the electrophotographic photoreceptor.
2. Related Art
In recent years, in image forming apparatuses utilizing electrophotographic methods, halftone reproduction has been demanded due to the requirements of colorization and high definition. Accordingly, in an electrophotographic photoreceptor (hereinafter, may be abbreviated as “photoreceptor”) used for image forming apparatuses, reproducibility of the halftone, namely, reproducibility of the exposure potential, is required.
Further, from the viewpoint of reduction in service costs, reduction in the frequency of replacement of the electrophotographic photoreceptor is required and, therefore, extension of the lifetime of the photoreceptors has become an important technical issue. Organic photoreceptors and inorganic photoreceptors are known as electrophotographic photoreceptors. Although organic photoreceptors are superior to inorganic photoreceptors in terms of cost or the like, organic photoreceptors are inferior to inorganic photoreceptors since the former have a short life due to abrasion of an organic photosensitive layer.
Thus, in order to lengthen the operating life of the organic photosensitive layer, provision of a protective layer with a high hardness and abrasion resistance on the surface of the organic photosensitive layer has hitherto been investigated.
Since a protective layer inhibits abrasion of the organic photosensitive layer, the lifetime of the organic photosensitive layer may be greatly extended. However, even if the protective layer has superior durability, it may be abraded with long-term use. For example, when a member such as a charging roll, a cleaning blade, or an intermediate transfer medium, which is directly in contact with the photoreceptor, is disposed at the periphery of the photoreceptor, or when hard particles such as silica or cerium oxide are used as an external additive for toner, the protective layer may be abraded.
Further, when a protective layer is provided at the surface of an organic photosensitive layer, and is irradiated with light emitted from a monochromatic light source such as a laser diode or light emitting diode, the irradiation causes reflection of light at the interface between the protective layer and the organic photosensitive layer. The occurrence of light reflection means that the amount of light is reduced when light incident on the surface of the photoreceptor reaches the photosensitive layer.